1. Field of the Invention
The present invention relates to a control unit, a plug-in unit, a transformer, a zero-phase current transformer, and a frequency measuring circuit which are preferably applied to a control center serving as a type of console in a control system for an electric power system.
2. Description of the Prior Art
FIG. 1 is a perspective view showing an appearance of a control center. The control center includes a plurality of control units 200 layered in a control center box 300. FIG. 2 is a perspective view of the control unit 200 as seen from a front face thereof, FIG. 3 is a perspective view as seen from a back face thereof, and FIG. 4 is a plan view as seen downward. Further, FIG. 5 is a sectional view taken along a line V--V of FIG. 1, showing the control center box 300. As shown in each drawing, side plates 1 and 2 are provided on both sides of the control units 200. A front transverse member 3 is disposed on the front side of a top of the side plates 1, 2, and a back transverse member 4 is disposed on the back side of the top thereof. A power source grip 5 is attached to the back transverse member 4.
A substantially Z-shaped equipment mounting plate 6 is disposed between the side plates 1 and 2 for attachment of various equipment. A circuit breaker 7 is attached to a left-side mounting portion of the equipment mounting plate on the front side of the control unit 200, and an operating transformer 10 having a substantially cubic structure and a current transformer 11 are attached thereto on the back side of the control unit 200. The operating transformer 10 serves as a power source for control in the control unit 200. An electromagnetic switch 8 and a current sensor 9 are attached to a right-side mounting portion on the front side of the control unit 200, and a zero-phase current transformer 12 is attached thereto on the back side of the control unit 200 to transform zero-phase current in line current. A guide rail 50 is attached to each outside of the side plates 1 and 2. Further, an operating handle 13 is attached to the front side of the unit to control the circuit breaker 7, and a terminal block 14 for control wiring is also attached to the front side of the unit.
As shown in FIG. 5, the control unit 200 is mounted in a housing 61 of the control center box 300 to have a unit door 62 on the front side thereof. A vertical bus 69 contacts the power source grip 5 to feed power to each control unit 200. The vertical bus 69 extends vertically in the control center box 300. In general, as shown in FIG. 6, main circuit wiring is established in the control unit 200 in the order of the power source grip 5, the circuit breaker 7, the current transformer 11, the current sensor 9, the zero-phase current transformer 12, and the electromagnetic switch 8.
FIG. 7 is a front view showing a mounting portion of the conventional power source grip 5, that is, the plug-in unit. FIG. 8 is a plan view partially broken away of the plug-in unit, and FIG. 9 is a sectional view taken along a line IX--IX of FIG. 8. FIG. 10 is a perspective view of the control unit 200, illustrating a plug-in unit portion in detail. FIG. 11 is a plan view of the control unit 200 shown in FIG. 10. An overcurrent relay 42 is also indicated in FIG. 10.
The plug-in unit includes a first insulating case 41, an elongatedly cover-shaped second insulating case 42 in which the first insulating case 41 is fitted, a lead wire 44, and a terminal 45. Three prismatic portions 41a and a connecting substrate portion 41b are integrally mounted to form the first insulating case 41. Three prismatic portions 41a respectively realize the power source grip 5. The prismatic portion 41a includes a square hole-shaped chamber 41c, and an extending rod 41d vertically extends in the prismatic portion 41a through the chamber 41c. The prismatic portion 41a contains a U-shaped contact 43 having elasticity. The U-shaped contact 43 includes a base portion 43a, a pair of contact legs 43b upward extending in parallel from the base portion 43a to be inwardly inclined in the course of the extension, and a distal end 43c whose distal end is curved to outwardly extend. A flange portion 41e is mounted on a periphery of the connecting substrate portion 41b. Further, a mounting hole 41f is provided in the connecting substrate portion 41b.
An end surface of a cylindrical extending portion 41g of the first insulating case 41 contacts an inner bottom surface 42a of the cover-shaped second insulating case 42. A side portion 42b of the second insulating case 42 contacts side surfaces of the flange portion 41e and the extending portion 41g. In this way, the first insulating case 41 is fitted with the second insulating case 42. In this case, the base portion 43a of the U-shaped contact 43 contacts the inner bottom surface 42a of the second insulating case 42. An extending portion 42c extends from the second insulating case 42 on the side opposite to the inner bottom surface 42a. A through-hole 42d is provided in the extending portion 42c. Further, a concave groove portion 42e is provided in the second insulating case 42 at a position to contact the U-shaped contact 43. Further, a mounting hole 42f is provided in a bottom portion of the second insulating case 42.
One end of the lead wire 44 is connected to the outside of the base portion 43a of the contact 43 by resistance welding, and the other end is connected to the terminal 45 with pressure.
A description will now be given of an assembling method of the plug-in unit. First, the contact 43 is inserted into the chamber 41c from the side of the extending portion 41g of the first insulating case 41. Next, the lead wire 44 passes through the through-hole 42d of the second insulating case 42, and thereafter the first insulating case is fitted with the second insulating case 43.
The lead wire 44 exits the plug-in unit assembled as set forth above to pass through a through-hole 6a in the mounting plate 6. The plug-in unit is inserted into a concave portion 4a provided in the back transverse member 4. Further, a fixing screw 53 is screwed into the mounting holes 6b, 42f, 41f, and 4b. The mounting hole 6b is provided in the mounting plate 6. The lead wire 44 is bundled by a wire bundling member 54. The terminal 45 is secured to the circuit breaker 7.
FIG. 12 is a top view of a conventional operating transformer 10, FIG. 13 is a left side view thereof, and FIG. 14 is a plan view thereof. In the respective drawings, reference numeral 98 means a primary coil, 99 is a secondary coil, and 100 is a tertiary coil. Reference numeral 101 means a terminal of each of the coils 98, 99, and 100, and 102 is a core. Specifically, reference numeral 102a means a top core, and 102b is a bottom core. The core 102 is formed by laminating plates punched out from a thin plate. Reference numeral 103 means a pressing plate which is disposed on both sides of the core 102, and the pressing plate 103 is fixed on the core 102 by a screw 104 to maintain a compression state of the core 102. Reference numeral 103a means a mounting leg formed by folding a bottom portion of the pressing plate 103 to have an L-shaped structure. A notch portion 103b is provided in the mounting leg 103a, and a screw passes through the notch portion 103b to fix the operating transformer 10.
FIG. 15 is a connection diagram showing an exemplary connection in the operating transformer 10. Voltage of 200 or 400 V is applied across U-V1, or U-2V of the primary coil 98. Then, voltage of 100 V can be derived from between 1u- 1v or 2u-2v of the secondary coil 99, and voltage of 18 V can be derived from between a-b of the tertiary coil 100.
As shown in FIGS. 12 to 14, the primary coil 89, the secondary coil 99, and the tertiary coil 100 are layered. Therefore, a height H of the operating transformer 10 is equal to a number obtained by adding the sum of heights of three coils to the heights of the top core 102a and the bottom core 102b.
FIG. 16 is a front view showing a conventional zero-phase current transformer 12. FIG. 17 is a sectional view taken along a line XVII--XVII of FIG. 16. Here, a circular zero-phase current transformer is shown.
As shown in the drawing, the circular zero-phase current transformer includes an annular coil portion 130, and a cable inserting aperture 139a serving as a space inside the coil portion 130. The coil portion 130 includes an annular core 134 made of a magnetic material having high magnetic permeability, a vibration isolating material 135 covering the core 134, a containing case 136 containing the core 134 and the vibration isolating material 135, a winding (secondary winding) wound on the containing case 136, and an insulating material 138 covering the winding 137.
Three-phase lines (primary conductor) 132a, 132b, and 132c corresponding to a primary winding pass through the cable inserting aperture 139a. Signal voltage according to ac current in the primary conductors 132a, 132b, and 132c is outputted through magnetic coupling to a lead wire 133 connected to the winding 137.
When the above circular zero-phase current transformer is mounted in the control unit or the like, the control unit or the like requires a space according to an outer dimension of the circular zero-phase current transformer. In a case where the space in the control unit or the like is limited, a track type zero-phase current transformer may be employed. In the track type zero-phase current transformer, three primary conductors 132a, 132b, and 132c are inserted into the cable inserting aperture 139a to be aligned with each other.
FIG. 19 is a block diagram showing a structure of a conventional frequency measuring circuit which is applied to the control unit and so forth. In the drawing, reference numeral 141 designates a line, 142A and 142B are voltage transformers respectively taking voltage having each different phase in the line 141, 144A is a first comparator to convert A-phase input voltage from the voltage transformer 142A into a rectangular wave, and 144B is a second comparator to convert B-phase input voltage from the voltage transformer 142B into the rectangular wave. Reference numeral 146A designates a counter to count a time for one period of the rectangular wave outputted from the first comparator 144A, 146B is a counter to count a time for one period of the rectangular wave outputted from the second comparator 144B, and 147 is a microcomputer to compute a frequency depending upon counted values of the counters 146A and 146B.
A description will now be given of the operation with reference to a timing diagram of FIG. 20. For example, an A-phase and a B-phase are deviated with a phase difference of 60 degrees. The frequency measuring circuit measures a frequency of one phase, for example, the A-phase. That is, an input port of the microcomputer 147 is connected to the counter 146A so as to receive the counted value of the counter 146A as input. The A-phase input voltage serving as sine-wave voltage as shown in FIG. 20(A) is fed to one input terminal of the first comparator 144A from the voltage transformer 142A. Reference voltage is fed to the other input terminal of the first comparator 144A. The reference voltage means voltage, for example, corresponding to voltage at a zero-cross point of the input voltage. In the following description, it must be noted that the first comparator 144A provides a high level output when an instantaneous value of the A-phase input voltage is greater than the reference value as shown in FIG. 20(H).
The counter 146A counts a reference clock to feed the microcomputer 147 with a counted value for a period from a rise to the next rise of output from the first comparator 144A. That is, the counted value corresponds to the period of the A-phase input voltage. The microcomputer 147 obtains the period of the A-phase input voltage depending upon the counted value from the counter 146A, and a frequency of the reference clock fed to the counter 146A. Further, the microcomputer 147 can obtain a frequency of the A-phase input voltage, which is the reciprocal of the period.
In a case where the A-phase voltage is interrupted due to occurrence of accident and so forth, if the other phase is available, it is necessary to continue frequency measurement of line voltage with respect to the available phase. Therefore, in such a case, the input port of the microcomputer 147 is switched over to the counter 146B on the side of the B-phase as another input source. The second comparator 144B is operated as in the case of the first comparator 144A to output a rectangular wave of a frequency corresponding to a frequency of the B-phase input voltage. The counter 146B is operated as in the case of the counter 146A to output a counted value corresponding to a period of the B-phase input voltage. Thus, the microcomputer 147 continues the frequency measurement with respect to the B-phase input voltage. As set forth above, the frequency measuring circuit can carry out the frequency measurement by using the dual input to the microcomputer 147, that is, after the measuring object is switched over to the available phase at a time of the accident.
Japanese Patent Publication (Kokai) No. 5-273265 discloses a frequency measuring circuit to measure the frequency after binarization of the input voltage by the comparator.
In the conventional control unit 200, wiring is established as shown in FIG. 6, that is, in the order of the power source grip 5, the circuit breaker 7, the current transformer 11, the current sensor 9, the zero-phase current transformer 12, and the electromagnetic switch 8. Thus, there is a complicated wiring path as shown in FIG. 4, resulting in an extremely defective operational efficiency. Further, since the zero-phase current transformer 12 is attached to a right-side back face of the mounting plate 6 in the unit, a limitation is imposed on a depth dimension of the electromagnetic switch 8 attached to a right-side front face of the mounting plate 6. As a result, the control unit 200 can not accommodate a bulk electromagnetic switch 8. It is necessary to extend a size of the control unit 200 so as to contain control equipments such as electromagnetic relay. Further, since the operating transformer 10 and the current transformer 11 are attached to a left-side surface of the mounting plate 6, a burning accident of the operating transformer 10 may result in burning of the current transformer 11.
Since the conventional plug-in unit is provided as shown in FIGS. 7 to 9, it is possible to pass the lead wire 44 through the insulating cases 41, 42 in assembly. The terminal 45 can not be attached before the lead wire 44 passes through the insulating cases. Further, when the plug-in unit is attached to the control unit 200, the lead wire 44 must pass through the through-hole 6a of the mounting plate 6. That is, an operational efficiency is extremely defective. Besides, there is a problem in that a space to mount each equipment is reduced since the lead wire 44 and the passing members extend from a surface of the mounting plate 6.
As shown in FIG. 5, a dimension in a depth direction of the control unit 200 is defined by the sum of a height of the circuit breaker 7 and a height of the operating transformer 10. Consequently, the most downsized possible operating transformer 10 has been desired in order to downsize the control unit 200, and reduce an area required for mounting.
The track type zero-phase current transformer 12 requires a more reduced height in the space required for mounting than that in case of using the circular zero-phase current transformer. However, in this case, since a width in the required space is more increased so that the mounting may be difficult. In addition, since the primary conductors 132a, 132b, and 132c are in alignment with each other, a balance characteristic required for the zero-phase current transformer may be deteriorated.
The conventional frequency measuring circuit requires the counters 146A and 146B corresponding to the respective phases. Additionally, there is another problem in that the input port of the microcomputer 147 should be switched over to another input source after detecting that voltage having a currently measured phase is interrupted.